1. Field of the Invention
The invention relates in general to a field of circuit layout, and more particularly to a symmetrical circuit layout structure and method.
2. Description of the Related Art
Recently, electrical products tend to have higher efficiency and smaller sizes. Thus, the electrical devices tend to be mounted in these electrical products in a denser manner. In order to mount the electrical devices in a denser manner, bare semiconductor chips are often mounted to a surface of a circuit layout board (PCB) in a flip-chip mounting manner. Specifically speaking, it is preferred to use a multi-layer circuit layout board to obtain the advantage of the high-density circuit layout because a semiconductor chip has a lot of connector pins. The semiconductor package, which may include the semiconductor chip, is an essential component in the electric circuit and is thus mounted on a PCB. The PCB may also be a multi-layer circuit layout board such that the high density circuit layout may be achieved.
FIG. 1A is a schematic diagram showing a conventional circuit layout structure. The circuit layout of FIG. 1A has the problem of electric characteristic asymmetry.
FIG. 1B is a schematic diagram showing another conventional circuit layout structure, wherein a number of ground wires and a number of signal wires are placed on the same metal layer, and the signal wires transmit several pairs of differential signals with the phase difference of 180 degrees. The circuit layout structure, which looks like a symmetrical structure, has the drawback of the enlarged area when the numbers of the signal wires and ground wires are increased.